Early on in Kathryn Bigelow's surfers-and-bankrobbers thriller Point Break, rookie wave-rider Keanu Reeves breaches a cardinal tenet of surf-rat etiquette by stepping into another man's wave. Bad idea. They collide and both wipe out horribly. As Reeves emerges dazed and breathless from the foam, the offended surfer swims toward him and punches him hard in the face. As he swims out again, he looks over his shoulder and delivers a deathless insult that indicts Reeves's perceived amateurishness, his essential hickhood, and his thousand-percent lameness: "Get back to the Valley, man! "

To hear people tell it, the San Fernando Valley has never been cool, never even come close. In southern California terms, it's long been a patronising synonym for everything that's the polar opposite of cool. It is to LA, its parent conurbation, what north New Jersey and Long Island are to Manhattan: far from the main action, way back in the boonies, the place where the maids and the pool cleaners live because they can't afford those steep uptown rents, and all-round shorthand for dweeb, geek, butthead and dipshit.

When John Travolta and Samuel Jackson find themselves with a friend's brains all over their car's upholstery in Pulp Fiction, they're stuck in the Valley. "Man, I ain't got no motherfuckin' contacts in 818!" howls Jackson, citing the Valley's area-code. If he didn't need help right now, if he was back in a bar in Inglewood with his boys, those words would be uttered with unconcealed pride.

But just as The Sopranos has recently lent an unexpected cultural cachet to the characterless, mall-blighted landscape of north Jersey, so too is the Valley acquiring its share of intoxicated residents, like Magnolia director Paul Thomas Anderson, eager to proselytise on its behalf, to hymn its lily-white weirdness, and mine its rich seams of inch-deep history and suburban surrealism.

The San Fernando Valley is actually, in legal terms, a part of the city of Los Angeles; but it's a distinctly separate place, cut off both mentally and geographically from the fleshpots of Hollywood, the corporate eyries of downtown LA, and the Speedo-clad, Coppertone-marinated democracy of the city's 40-mile ribbon of golden beaches. The catalogue of differences extends to the Valley's beleaguered suburban homesteader mindset, its near-Iowan racial homogeneity, and even its climate. The Santa Monica mountains which form the Valley's southern boundary help shield it from the coastal breezes that cool Los Angeles proper, and in summer it's never less than 10 degrees hotter, and exponentially more humid.

The Valley - LA's neglected stepchild - has something of a municipal inferiority complex. LA politicians hold its purse strings, and Valley powerbrokers have long complained about getting short shrift when it comes to the disbursement of funds. For a few years now there has been a small but growing movement to secede from Los Angeles and establish a separate city. If that happened the resulting metropolis would be the nation's seventh largest, and by some considerable measure its whitest. And in the eyes of its detractors, the most boring.

Those are the cliches. Closer examination reveals that in many ways, the history of southern California is better encapsulated by the Valley than by LA itself. From orange grove to urban nightmare, it is truly a place shaped by the 20th century, its destiny inextricably intertwined with the great technological advances of the last 100 years: aviation, the automobile, the movies and TV (and their bastard offspring, the porn industry), space flight, defence manufacturing and massive residential housing developments. And without the massive engineering project that brought water to LA from the Owens River Valley in the mid-teens, and the invention of the affordable air-conditioning unit after the second world war, the Valley (and much of the American southwest) as we know it might never have come into being.

As anyone who's seen Chinatown knows, the powerbrokers of LA essentially stole the Owens Valley water supply. Today the once fertile area is a dustbowl. William Mulholland, head of LA's Department of Water and Power (Chinatown's original title was Water and Power), in concert with an informal consortium of super-wealthy Angelenos, including Los Angeles Times owner Otis Chandler, agitated for a municipal bond issue to finance the 200 miles of aqueducts and pipelines needed to bring the water to the city.

Earlier, they had secretly bought huge parcels of then arid Valley land at rock-bottom prices, knowing the killing they'd make when irrigation and agriculture became feasible. The San Fernando Valley's very existence is thus based on a massive act of environmental piracy, a gigantic landgrab and a kind of Wild West boomtown corruption. The taxpayers of LA thus paid dearly for the means to enrich even further its very wealthiest robber barons.

On the other hand, no water, no city. For better or worse, it takes visionary, greedy bastards like these to build cities where before there were only sand and rattlesnakes. And from the 1920s until the beginning of the second world war, the Valley was something like a paradise. This mythical heaven could not last though. It was hustled out of existence by industrialisation and the outbreak of war.

Industrial growth was hugely spurred by the need for ships and weapons with which to fight the Pacific campaign. The sudden influx of steel plants and armaments manufacturers (and the rise of the automobile) poisoned the air and led to agriculture's steep decline. Before and during the war, farmland and unincorporated tracts were bought up en masse by prescient developers and private investors (perhaps the most famous were Bing Crosy and Bob Hope) in preparation for the need to house millions of returning GIs. Demobbed in Long Beach or San Pedro, Okie soldiers who'd starved during the Depression took one look at the sunshine and the limitless possibilities and never went home.

Financed by cheap loans available through the postwar GI Bill, the Valley started to fill up. The new cities didn't emerge organically, though. Huge amalgamations of erstwhile farmland were subdivided into streets and neighbourhoods by massive development and construction corporations. The period is well portrayed in the sequel to Chinatown, The Two Jakes, much of whose action takes place in a model home on such a development. Where its lawn ends, there the desert begins, and periodically the ground underfoot emits terrifying tremors.

Be that as it may, the 1950s are now fondly remembered as the second period in which the Valley was close to very heaven. Returning GIs and those Easterners who made the trek west after Eisenhower's 1955 Federal Highways Act linked up the country found more space than they could have imagined back in their cramped eastern and midwestern tenements and farms. With Depression and war fading from their memories, they built a life of swimming pools, backyard barbecues and two-car garages, becoming a new version of Thomas Jefferson's ideal American, the freeholding yeoman-farmer (or yeoman-worker bee) in a landscape of single-family dwellings.

But as urban theorist Mike Davis has pointed out, this "endless summer" was a whites-only phenomenon: restrictive covenants were the order of the day. If you signed a property deed, it was likely to include the phrase "No one whose blood is not entirely of the Caucasian race will be permitted to own property in this subdivision." Hence the number of primarily Jewish enclaves that inserted themselves in the cracks between such racially monitored new cities. Throughout the 1960s Klan membership in southern California was highest in the Valley.

In the 1970s the Valley's only unifying political issues were its opposition to the busing of black children to white Valley schools, and the passage of Proposition 13, which aimed to cut disproportionate property taxes, but ended up starving California's schools and infrastructure. And more recently Rodney King was beaten up on the Valley's Foothill Boulevard as 17 policemen watched. Just up the freeway is the Spahn Movie Ranch near Chatsworth, whence Charles Manson - another avowed white supremacist - dispatched his robot-hippie murderers on their dreadful missions.

The spectre of tackiness reared its ugly head again in the late 1970s, when it became apparent that the Valley was suddenly America's porn headquarters. Back then, in the period covered by Paul Thomas Anderson's epic Boogie Nights, "the Industry", as it is euphemised by its participants was made up of tiny owner-operated companies, some with a foot in gangland, filming on the lam and making a packet.

The video revolution did to porn what the CD did to the music industry and since the mid-80s the small fry of years gone by have grown into immensely rich entrepreneurs with names like John "Buttman" Stagliano, Max Hardcore, John T Bone and Seymour Butts. The upshot - despite the occasional kerfuffle over backyard sex-shoots - is a semi-respectability that's prompted a surreptitious, previously inconceivable crabwalk into the fringes of the mainstream.

Without equating the area solely with porn - though plenty of folks do - the Valley itself has also recently become cooler than once it was. America's late discovery of irony hasn't hurt - ie, liking something for the very reasons other people despise it - and neither have a slew of movies like California Man (in which a defrosted caveman is capable of becoming Prom King), and Todd Haynes's Safe, which proves that the spirit of Michelangelo Antonioni can be invoked in these unpromising surroundings. And the wildly underrated Two Days in the Valley makes eloquent use of a slew of Valley stereotypes and grotesques.

If there is a single sight that sums up the Valley for me, it is a swimming pool I once visited in the town of Tarzana, which was originally an estate founded by Edgar Rice Burroughs in 1911 and named for his most famous creation. It was the first pool ever built in the San Fernando Valley, and was a gift to Burroughs from Otis Chandler, made possible in part by his sudden enrichment after the water hijack in 1913. When I saw it a few years ago, it was just a trash-filled, tiled hole in the ground.

For me it represents both the Valley's freebooting, obscenely wealthy origins, and its potential apocalyptic future conjoined in a single image. Five well-placed bombs on the Owens Valley pipeline and the whole region might soon seem this desolate, with the city that shouldn't be here slowly reclaimed by the desert, and jaguars once again roaming Magnolia Boulevard. A mile or so away Burroughs is buried under a tree outside his old house. Ten feet from his resting place, the traffic roars by on Ventura Boulevard.

The Valley, like much of California, is a state of mind made up of equal parts false memory and outrageous optimism. It contains as many defoliated Edens as it does the remnants of utopias strangled in their cradles. The Valley is dead; long live the Valley!

 Magnolia is released on March 17.

Valley movies

California Man

Two semi-literate Valley teenagers defrost a caveman (the always hysterical Brendan Fraser) - and he feels right at home.

Chinatown/The Two Jakes

The murky history of the San Fernando Valley's origins, in violent detail.

Boogie Nights

A sprawling epic of the late 70s and 80s Valley porn industry - and about the first movie that does not despise and condescend to the place.

Two Days in the Valley

Midnight-black comedy thriller that takes every imaginable Valley stereotype and chucks them into a boiling stew of murder plots, ripoffs and double-crosses.

Safe

Queasy portrait of a bourgeois Valley housewife (Julianne Moore) who contracts an undiagnosable ailment. I think what's doing her in is the Valley itself.